src.cpp: In function 'bool ktra(long long unsigned int)':
src.cpp:5:31: error: 'cuoi' was not declared in this scope
unsigned long long giua,dau=1;cuoi=n;
^
src.cpp:9:22: error: 'x' was not declared in this scope
if (a[giua]==x)
^
src.cpp: In function 'int main()':
src.cpp:22:10: error: 'i' was not declared in this scope
for (i=1;i<=n;i++) fin>>a[i];
^